全文获取类型
收费全文 | 139篇 |
免费 | 78篇 |
国内免费 | 7篇 |
专业分类
化学 | 21篇 |
力学 | 23篇 |
数学 | 3篇 |
物理学 | 177篇 |
出版年
2023年 | 8篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 2篇 |
2017年 | 10篇 |
2016年 | 21篇 |
2015年 | 9篇 |
2014年 | 16篇 |
2013年 | 5篇 |
2012年 | 8篇 |
2011年 | 10篇 |
2010年 | 8篇 |
2009年 | 15篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 4篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1984年 | 2篇 |
排序方式: 共有224条查询结果,搜索用时 768 毫秒
111.
为解决水声目标小样本模式识别问题,有效地提高复杂海洋环境中的识别精度,提出了一种基于经验模式分解(EMD)、特征距离评估技术(FDET)和组合支持向量机(CSVMs)的水声目标智能识别方法。首先,将滤波、Hilbert包络解调和EMD等信号处理方法对水声目标的辐射噪声信号进行预处理,提取7个包含原始信号和预处理信号的时域和频域统计特征的特征集。然后,通过FDET从原始特征集中选择出7个敏感特征集。最后,将7个敏感特征集输入到7个支持向量机分类器中,利用遗传算法对7个分类器的结果进行合并,构成CSVMs分类器,从而实现对水声目标的智能识别。将该方法应用于舰船等水声目标的识别中,研究结果表明,该方法的识别性能优于单一SVMs分类器:同时,经过FDET得到的敏感特征集能明显地提高识别精度。 相似文献
112.
113.
114.
The fluid forces resulting from wave interaction with large submerged structures may be calculated using numerical procedures based on the solution of the associated boundary-value problem. In this paper, the analysis of wave interaction with a fixed submerged object of arbitrary cross-section and infinite length using a two-dimensional boundary value formation based on linear diffraction theory is summarized. Subsequently, the application of the boundary element method to obtain a solution is presented. The numerical considerations are emphasized with particular reference to computational efficiency. Numerical results are presented in the form of dimensionless wave force plots for various structural shapes. In the case of a bottom-seated half cylinder, for which there exists a closed-form solution, comparisons are made between results generated using both boundary element and equivalent finite element approaches. In the case of a submerged cylinder, comparisons are made between boundary element derived values and experimental results. The boundary element results compare well with both the closed-form solution and the experimental values. 相似文献
115.
Saito T. Marumoto M. Yamashita H. Hosseini S.H.R. Nakagawa A. Hirano T. Takayama K. 《Shock Waves》2003,13(2):139-148
The attenuation of an underwater shock wave by a thin porous layer is studied both experimentally and numerically. The shock waves are generated by exploding 10 mg silver azide pellets and the pressures at different distances from the explosion center are measured. Measurements are also carried out with a gauze layer placed between the explosion source and the pressure gauge. The results with and without the gauze layer are compared evaluating the shock wave attenuation. Numerical simulations of the phenomenon are also carried out for a simple wave attenuation model. The results are compared with the experimental data. Despite the simple mathematical model of wave attenuation, the agreement between the experimental and numerical results is reasonable.Received: 22 October 2002, Accepted: 17 June 2003, Published online: 5 August 2003PACS:
47.11.+j, 47.40.Nm, 47.55.Mh 相似文献
116.
117.
This paper is concerned with membrane analysis and optimal design of submerged domes. In addition to hydrostatic pressure,
domes are also subjected to selfweight and skin cover load, which are invariably present in these types of structures. Using
the membrane theory for thin shells and by adopting a fully stressed design, equations governing the meridional curve of submerged
domes are derived with allowance for selfweight and skin cover load. A set of nonlinear differential equations, which correspond
to a two-point boundary problem, is solved by the shooting-optimization method. Based on a family of fully stressed designs
associated with a given water depth and dome height, the optimal dome shape for minimum weight is determined. 相似文献
118.
S. Manneville A. Maurel P. Roux M. Fink 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):545-549
We report new results on the ultrasonic characterization of a fluid flow using an acoustic time-reversal mirror (TRM). The
structure of a large vortex generated by a rotating disk in a hollow cylinder is investigated both inside and below the cylinder.
For mean-flow characterization, the TRM is shown to be a powerful vorticity detector. Experimental time-of-flight data are
successfully compared to a numerical simulation of the flow and the orthoradial velocity is reconstructed using simple geometrical
acoustics. Real-time measurements allow us to extract the precession motion of the vortex, providing direct, non-intrusive,
and dynamical information on the flow.
Received 23 April 1998 相似文献
119.
The present paper describes experimental investigation on the flow pattern and hydrodynamic effect of underwater gas jets from supersonic and sonic nozzles operated in correct- and imperfect expansion conditions. The flow visualizations show that jetting is the flow regime for the submerged gas injection at a high speed in the parameter range under consideration. The obtained results indicate that high-speed gas jets in still water induce large pressure pulsations upstream of the nozzle exit and the presence of shock-cell structure in the over- and under-expanded jets leads to an increase in the intensity of the jet-induced hydrodynamic pressure. 相似文献
120.
为了改善主动光在水下传播过程中由散射与吸收效应导致的深海图像对比度低下以及颜色失真问题,提出一种水下图像增强算法.不同于传统方法利用最亮点的强度值作为背景光,提出基于物体与背景光非相关性的背景光估计方法,有效避免了前景处的亮像素或白色物体像素对背景光的误判,同时确保了去散射的精确性,提高水下图像的对比度;针对人造光源的颜色增益和光路衰减导致的图像色偏等问题,在去散射图像上选取离光源最近的灰色像素,利用其对光源的敏感性,将光照强度分离出来.最终,通过估计并去除光源本身的颜色增益,同时补偿光在传播过程中的损失,实现图像的颜色校正.实验结果表明,所提算法可以有效去除水下图像的散射效应,较好地恢复图像色彩,进而获得较优的增强图像.相比于其他算法,增强后的图像信息熵和水下图像质量评价指标值较高,说明该算法能显著提升水下图像的质量,同时保留图像有用信息. 相似文献